1. Field of the Invention
The present invention relates generally to paint film thickness of painted bodies and, more specifically, to a method of determining waveform stability for a pulse echo layer thickness transducer used for measuring paint film thickness of painted bodies.
2. Description of the Related Art
The application of paint to a body of a vehicle is a sensitive process. The quality, durability and color matching of the paint are critical in producing a high quality product, and therefore require significant quality control efforts. Generally, paint film thickness is monitored by use of hand-held sensors, such as an ultrasonic pulse echo layer thickness (PELT) transducer. These sensors are handled by an operator who must manually apply the sensor against the surface of the painted body of the vehicle in a position normal to the surface at a plurality of locations on the surface to measure the paint film thickness. In the performance of this measurement, it is highly important that the operator position the sensor normal to the particular location being sensed, and it is also critical that the operator position the sensor consistently at the same plurality of locations on the surface being sensed. Errors in the angle of the sensor relative to the surface or in the location of the sensor on the surface can adversely affect quality control. Because a significant reliance is placed upon the operator, a significant amount of error is introduced in the quality control process.
The PELT transducer used for paint film thickness measurements receives signals from successive paint layers. Determining the stability of the signals that are reflected by the paint layers is important before any thickness measurements are conducted using the PELT transducer. A waveform is considered to be stable if a measure used for comparing two successive waveforms exceeds a certain threshold, and the measure does not change significantly over a series of successive waveforms. Previously, human judgment was used as a determining factor for identifying a possible stable waveform on the PELT transducer.
As a result, it is desirable to provide a method for determining as to when signals from a PELT transducer have reached steady state under the given specifications automatically. It is also desirable to provide a method for determining waveform stability for a PELT transducer used for measuring paint film thickness on a painted body of a vehicle. It is further desirable to provide a systematic method for determining stabilization of signals reflected from paint layers of a vehicle body using a PELT transducer.
Accordingly, the present invention is a method of determining waveform stability for a pulse echo layer thickness (PELT) transducer used for measuring paint film thickness of painted bodies on a vehicle. The method includes the steps of reading a signal with the PELT transducer with respect to a desired location of the vehicle. The method also includes the steps of determining whether a maximum absolute value of the read signal is greater than a noise threshold (xcfx86) and computing a measure (xcfx81) based on an option (k). The method includes the steps of determining whether the computed measure (xcfx81) is above or below a predetermined threshold (T) based on the option (k), and concluding a stable/unstable signal from the PELT transducer.
Some of the associated advantages with the method of the present invention include automatic waveform stability detection, fast and accurate performance, enhanced ergonomics (no need for visual information) if used by a human operator, and easily implementation in a robotic sensor.
Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.